DICE and AMD have made available a new game update for Battlefield 4, which brings the Mantle renderer.

Mantle is a new low-level graphics API and it is a major change and improvement to how dvelopers are able to program & use modern GPUs in order to get the most out of them.

Battlefield 4 on PC is already quite heavily optimized using DirectX 11 and DirectX 11.1, but with Mantle the game's developers have managed to significantly reduce CPU cost in their rendering, efficiently parallelized it over multiple CPU cores and reduce overhead in many areas.

The biggest performance gains can be seen when the game is bottlenecked by the CPU which can be quite common even on high-end machines.

If you have the above you will see a new "Graphics API" option in the in-game Graphics Options settings after starting the game, here you can switch between using DirectX 11 and Mantle (remember to restart the game after changing).
To compare performance with Mantle vs DX11 Frostbite devekopers have done a couple of benchmarks with Battlefield 4 on 3 different configurations & test scenes: